I can't give this museum three stars because that is described as "average," and Roswell with it's Americana glory and quirky conspiracy is far from average - so four stars it is!
The museum is small and could be done in an hour, unless you want to stay for a movie screening (then allow time for an 1.5 hour film, too. The 10am film was the '94 flick Roswell with Martin Sheen, and I do wish I had time to sit and watch it. May that attest to how interesting the museum is.
Now, you need to treat the museum for what it is - this is a great American tale of cover up, conspiracy, military secrets and decades of legend; therefore, it isn't like they have artifacts to back everything up! What you can expect is a lot of newspaper clippings, copies of affidavits from witnesses, silly alien exhibits, and displays of related topics such as rocket development, skeptics claims, documented abductions and debunked UFO sightings.
The history was very interesting and actually well balanced, presenting initial statements, government explanations, timelines of events, etc. Because of the number of documents on the walls, it was hard to find the over riding summation of each section, so I feel like I missed a lot of major points. That is my main criticism of the museum.
The gift shop is very expensive for what is in there - try any number of other stores on the main drag. You can always come back to the gift shop.
Worth a visit. Check it out - a fun and unique sojourn into history, conspiracies and space/military black ops.